In the measurement and instrumentation literature and industry, the words gauge and gage can both be found to describe a pressure sensor or transmitter that measures relative to ambient pressure.
According to the Merriam-Webster dictionary: ”the word gage is a variant spelling of gauge, which in the noun form refers broadly to measurement (“fine-gauge wire”) or a standard by which something is measured (“polls are a good gauge of how voters might vote”).” The Merriam-Webster adds: “Gauge is by far the preferred spelling in general usage for both the noun and the verb; we encourage you use it.”
Gauge has become the most common word to describe a measuring device or a gauge pressure sensor measuring relative to ambient pressure.